Multi-path fading is a contributing factor to microwave radio receiver error rates. Its effects can be reduced by employing transmitters with multiple outputs and receivers with multiple inputs. Simulating the dynamic multi-path fading behavior of such multi-input, multi-output (MIMO) communication channels is necessary to properly characterize the microwave radio equipment.
The most general linear model for a MIMO multi-path fader is shown in FIG. 1. Each Filter (m,n) block represents a time varying filter. Any set of band limited signals can be down converted and sampled so the filtering may be applied using a discrete time digital filter operating on a complex (I/Q) data sequence. Generally, each filter is implemented as an independent Finite Impulse Response (FIR) filter with time-varying complex coefficients (taps). After filtering, the signals can be up-converted and reconstructed as continuous time waveforms.
The key parameters associated with this multi-path fader are: the number of input and output channels supported, the filter sample rate, the number of taps in each filter, the maximum rate at which the filter taps can be updated, and the precision of the filter math.